This invention relates to apparatus for providing clean air work areas, and more particularly, to an overhead module that provides a bounded, vertically flowing zone of clean air to a work area. The invention works in conjunction with filters to supply virtually contaminant-free air to critical production or laboratory areas.
In the present age of advanced technology, there is an increasing requirement for particulate-free and/or bacteria-free working environments. These environments are typically referred to as clean rooms or clean areas, and to provide such clean working areas with the required contaminant-free air it is a practice to circulate the air through a bank of one or more filters. In many clean areas, particles in the air must not exceed 100 particles larger than 0.3 microns per cubic foot of air. This high level of particulate filtration is achieved by the use of what are in the industry generally called "absolute" or "HEPA" filters. These filters are comprised of suitable filtering media, having corresponding efficiences, which are placed in a filter frame and sealed with adhesive to form a filter pack. The filter pack is in turn typically mounted and sealed into a supporting structure.
It is known to provide a workbench which has an air filtration system that delivers a horizontal zone of clean air beyond the normal work surface of the workbench. A clear air workbench of this character is disclosed in U.S. Pat. No. 4,016,809, issed Apr. 12, 1977 to Philip R. Austin. In this work center, the work area is confined between directive walls or panels thus severely limiting the flexibility of the working environment. The effect of gravity also eventually distorts the horizontal flow of clean air. Work centers or workbenches of the type disclosed in the prior art are thus limited in their application and are unsatisfactory for situations requiring an environment unrestricted of side walls, panels, etc., such as medical device manufacturing, optical equipment assembly lines, semiconductor production, sterile operating conditions, phases of the electronics industry, and other similar applications.
For the type of above mentioned applications conventional type downflow filter devices with vinyl curtains have been utilized. However, such known devices are also found to be unsatisfactory. Turbulence within the laminar flow area cannot be controlled, purging of generated particles within the laminar flow area cannot be effectively achieved, the direction of the laminar flow cannot be varied, and there is particle retention due to electrostatic conditions associated with the curtains. Furthermore the curtains are in general unsightly, must be periodically disinfected, cleaned, and replaced.
It is also known to provide a downflow filter device in which the vertical flow of filtered air is bounded by an air curtain. An example of a construction of this type is shown in German Offenlegungsschrift [laid-open application] No. 2,130,255. In this device the direction of the laminar flow, defined by the direction of the curtain of air, is fixed and cannot be varied for specific work applications and/or floor arrangements for the most efficient discharge and subsequent removal of filtered air. The curtain of air generated by the German device also does not use HEPA filtered air and thus because of eddy currents generated along the curtain of air, the German device cannot achieve cleanliness.
The present invention has overcome the inadequacies of the prior art by providing a vertical laminar flow filter module that creates maximum protection for a work area environment without sacrificing flexibility. The system incorporates a Class 100 (U.S. Federal Government Standard 209-b) working area with a HEPA filtered curtain of air that discharges downward around the perimeter of the primary filter area. The air curtain eliminates the requirement for vinyl curtains or directive walls or panels. The air curtain is discharged at a relatively high velocity in comparison to the laminar flow of air from the primary filters, thus creating a vacuum and positive pressure which protects against backwash and turbulence, and containing the primary laminar filtered air flow in a downward direction to the floor or other bottom surface. Contaminants are picked up by the vacuum action of the high speed air curtain and are expelled away from the clean laminar flow air by the positive pressure of the jet airstream. By virtue of this arrangement room air currents from any source carrying air-born contaminants are also prevented from entering and violating the work area. A proper balance of the two air streams assures optimal air flow at working levels and prevents contamination causing turbulence found in prior art laminar flow devices or systems when the primary air stream changes from vertical to horizontal flow.
According to the present invention, a vertical laminar flow filter module is provided with an adjustable air nozzle means for varying the direction and velocity of the air curtain. Therefore, it is an advantage of the present invention to provide an improved downflow type filter module that comprises a controllable air curtain for adapting to specialized applications, critical objects, floor slopes, floor materials, and the like. By directing the laminar flow downward from the overhead filter module, a virtually unrestricted clean work area is provided. Separate blowers and passage means are incorporated for the primary laminar flow filtered air and the HEPA filtered perimeter air curtain to provide maximum control of air velocities. Fluorescent lights, which may be located out of the main airstream to eliminate accidental breakage, are included.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying description.